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Painted Predator Antenna
- Thread starter tvaverde
- Start date
I know I cut at least a good 4 or 5 inches off. I'll try and remember to measure it for you tomorrow. Depending on your truck, a 22 inch shaft may not work. I have a 2011 super duty and my coil is just a few inches clear of the top of my cab. The 22 inch shaft wouldn't have worked for me. But I did loose a couple Inches mounting mine to my toolbox instead of to my actual bed rail.
Ok. I extended my shaft , just for grins.
I didn't want to go out and buy a longer shaft before doing some testing.
I got it above the roof about 10"
The total length of the bottom shaft is 27". The whip is trimmed down to 36"
This gave me the best SWR @ 1.8.
So if I go out and buy a 27" shaft that is made by Kale for this set up , will I get better numbers.
All input is welcome
Thanks for every body that has chimed in.
I didn't want to go out and buy a longer shaft before doing some testing.
I got it above the roof about 10"
The total length of the bottom shaft is 27". The whip is trimmed down to 36"
This gave me the best SWR @ 1.8.
So if I go out and buy a 27" shaft that is made by Kale for this set up , will I get better numbers.
All input is welcome
Thanks for every body that has chimed in.
UPDATE .
I spoke to Kale today. I am running 18' of RG213. He suggested to try RG8. So I took 18' feet of RG 8 and ran it along the out side of my truck and I was able to get my SWR's down to 1.4 across the band. So this weekend I will run the RG8 coax exactly how I have the RG213 run to see if its the coax itself or just the way I have it routed under my truck. That is giving me problems .
TO BE CONTINUED .
I spoke to Kale today. I am running 18' of RG213. He suggested to try RG8. So I took 18' feet of RG 8 and ran it along the out side of my truck and I was able to get my SWR's down to 1.4 across the band. So this weekend I will run the RG8 coax exactly how I have the RG213 run to see if its the coax itself or just the way I have it routed under my truck. That is giving me problems .
TO BE CONTINUED .
Something about this seems odd. You replaced the coax and now have a wider bandwidth? That is a sign that you now have worse coax (in terms of losses) than you did before.
I'm not sure if it is possible in your setup but can you hook that SWR meter up directly at the antenna feed point? Doing this will show the actual readings from the antenna itself. Coax has the ability to make the bandwidth the antenna operates at appear wider than it actually is at the radio end, although a run shorter such as 18 feet shouldn't have that much of an effect.
The DB
My Sirio performer pl5000 has 4 meters of rg58u. It's mounted to a Sirio 145 mag mount. A low SWR and wide enough for 10&11 meters.
Thanks for chiming in.
You lost me on bandwidth
When I changed the coax from a 213 to a RG8 I was able to get the SWR's down from a 1.8 to a 1.4. The only difference is I just routed the RG8 around and threw the window Instead of running it under my truck and through the floor like the 213.
I can probably hook up my SWR meter at the antenna , will this help eliminate the coax as being the problem by isolating the antenna ?
Sorry if this is a dumb question.
Thanks
Tony
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A coax upgrade often presents a worse SWR. This is because there is less loss in the upgraded coax, and coax loss makes the SWR readings look better than they actually are. Putting the meter at the antenna feed point eliminates these coax losses from the SWR reading and shows you the exact SWR for the antenna itself, which is really what is important.
That being said, there isn't much difference between RG-8 and RG-213. RG-213 is the current updated version of the former RG-8 standard, and specs very close. A .4 difference in SWR readings of what is in essence a very short run of two very similar coax's with similar specs sounds a bit high. (Not saying you did or said anything wrong, it just sounds high to me.) It should also be noted that 18 feet of either coax should have such a minimal effect on the SWR reading that it should be indistinguishable from a reading taken at the antenna (short of using much more sensitive equipment than a simple SWR meter).
Also a tip for measuring SWR, when comparing readings try and take comparison readings from the same spot, not moving the vehicles in between. The environment that you are in has an effect on the antenna. I have graphic analyzer, and if a car passes by 30 feet away while running the scan can see the difference the chart it makes. Birds flying by the antenna look like little spikes on the readout. Antennas are more sensitive to their surroundings than I think many people realize.
The DB
I don't think you can do any testing that will give you any pertinent information by using only your antenna, and swapping out the feed line. It can certainly show if there's a difference between them of some kind, but it can't tell you what that difference is. The simplest method I can think of to check a feed line's characteristic impedance is by using a dummy load (which also assumes that the dummy load is accurate). If you use your antenna, you are making an assumption that it is tuned to the 'ideal' 50 ohms and zero reactance, which is impossible to determine with only an SWR meter. Testing usually can do no harm, so if you want to do it, do it.
Considering the short length of the cable I don't see why you would see any differences other than very 'fractional' ones. The biggest differences between those two cables are their characteristic impedance and the amount of loss in the lengths used. The run is short enough that I honestly don't think you could measure those losses at all, the average meter is just not ever accurate enough (any meter!). If you are really hearing a difference, or seeing a difference on a meter of some kind, then that tells me that there's a 'problem' somewhere else. Small differences don't make any -practical- difference.
The routing of the cable shouldn't make any difference at all (keep the stuff off of the muffler or any moving parts!). If the total length of the cable is 'close', as in several feet, that shouldn't make any difference either. Of course, that assumes that the antenna really is 50 ohms and zero reactance, which is rare. The larger that reactance number the more differences there can be. An SWR meter wouldn't know a reactance is it was bitten by it, that's the biggest 'unknown'.
Ain't all this stuff fun??
- 'Doc
Considering the short length of the cable I don't see why you would see any differences other than very 'fractional' ones. The biggest differences between those two cables are their characteristic impedance and the amount of loss in the lengths used. The run is short enough that I honestly don't think you could measure those losses at all, the average meter is just not ever accurate enough (any meter!). If you are really hearing a difference, or seeing a difference on a meter of some kind, then that tells me that there's a 'problem' somewhere else. Small differences don't make any -practical- difference.
The routing of the cable shouldn't make any difference at all (keep the stuff off of the muffler or any moving parts!). If the total length of the cable is 'close', as in several feet, that shouldn't make any difference either. Of course, that assumes that the antenna really is 50 ohms and zero reactance, which is rare. The larger that reactance number the more differences there can be. An SWR meter wouldn't know a reactance is it was bitten by it, that's the biggest 'unknown'.
Ain't all this stuff fun??
- 'Doc
